Various types of gate arrays are well known in the art. Gate arrays comprise a multiplicity of transistors which are prefabricated. A specific application is achieved by customizing interconnections between the transistors.
Routing arrangements have been proposed for reducing the number of custom masks and the time needed to manufacture gate arrays by prefabricating some of the interconnection layers in two-metal layer gate array devices. Prior art devices of this type typically employ three custom masks, one each for the first metal layer, via layer and second metal layer.
U.S. Pat. No. 4,197,555 to Uehara describes a two-metal layer gate array device wherein the first and second metal layers are pre-fabricated and the via layer is customized. Uehara also shows use of pre-fabricated first metal and via layers and customization of the second metal layer.
U.S. Pat. Nos. 4,933,738; 5,260,597 and 5,049,969 describe a gate array which is customized by forming links in one or two prefabricated metal layers of a two-metal layer device.
U.S. Pat. No. 5,404,033 shows customization of a second metal layer of a two-metal layer device.
U.S. Pat. No. 5,581,098 describes a gate array routing structure for a two-metal layer device wherein only the via layer and the second metal layer is customized by the use of a mask.